Gas imaging systems and methods

ABSTRACT

An IR imaging device includes an optical element receiving infrared radiation from a scene, a filter blocking IR radiation outside of a particular range of wavelengths, an array of sensor pixels to capture an image of the scene based on infrared radiation received through the optical element and filter, the array of sensor pixels comprising a first array of sensor pixels to image gas in within a first spectral bandwidth, and a second array of sensor pixel to sense IR radiation in a second spectral bandwidth where gas is not detected, a read-out integrated circuit (ROIC) and logic circuitry to generate a first image sensed by the first array and a second image sensed by the second array, and gas detection logic to detect the presence of gas in the first image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/586,809 filed Sep. 27, 2019 entitled “GAS IMAGING SYSTEMS ANDMETHODS,” which is a continuation of International Patent ApplicationNo. PCT/US2018/025585 filed Mar. 30, 2018 and entitled “GAS IMAGINGSYSTEMS AND METHODS,” which claims priority to and the benefit of U.S.Provisional Patent Application No. 62/480,234 filed Mar. 31, 2017 andentitled “UNCOOLED CAMERA SYSTEM OPTIMIZED FOR OPTICAL GAS IMAGING,” andU.S. Provisional Patent Application No. 62/541,626 filed Aug. 4, 2017and entitled “DUAL COLOR HIGH SENSITIVITY INFRARED SENSOR FOR GASIMAGING,” which are all hereby incorporated by reference in theirentirety.

TECHNICAL FIELD

One or more embodiments of the present disclosure relate generally toinfrared imaging and, in particular, to gas detection and/orvisualization using infrared imaging systems and methods.

BACKGROUND

Infrared (IR) (e.g., thermal) images of scenes are often useful formonitoring, inspection and/or maintenance purposes, for example, formonitoring gas leaks at an industrial plant. An IR imaging device (e.g.,an IR camera, a thermal camera, etc.) can capture IR image datarepresenting infrared radiation emitted from an observed scene. Thecaptured IR image can be processed, displayed and/or stored away, forexample, in the IR imaging device or in a computing device connected tothe IR imaging device such as a tablet computer, a smartphone, a laptop,or a desktop computer.

IR imaging devices are used for detecting the presence of gas, forexample, in the form of a gas cloud or gas plume, and for producing avisual representation of the gas in an infrared image. A gas infraredimage can be used for visualizing and monitoring gas leaks, for example.However, detection of gas using conventional uncooled IR imaging systemsoften suffer from having too low of a sensitivity to detect gas below acertain gas particle concentration. For example, the contrast betweengas information and noise/interference and/or the contrast between gasinformation and the background modulation in a generated gas infraredimage may be too low to effectively identify gas in the image. Thecontrast between gas information and the background modulations may beimproved with the inclusion of a narrow bandpass filter, but noise isproportionally increased as a result of this change. For conventional IRimaging systems, there is typically no bandwidth that has a sufficientlyhigh enough gas-background/span contrast and gas-noise contrast. Thesensitivity may be further reduced by various physical aspects, such asvarying temperatures and emissivity in the observed scene background,noise, other gases, aerosol particles, and moving gas clouds.

One approach for an IR imaging device to improve the ability to detectgas and reduce noise is to implement a cooled IR detector, where theimaging sensor is integrated with a cryocooler. The cryocooler lowersthe sensor temperature to cryogenic temperatures, with the reduction insensor temperature effectively reducing thermally-induced noise.However, cooled IR imaging devices are fragile, large in size, slow,costly, and difficult to use in hazardous locations. Thus, there is acontinued need to improve the gas sensitivity of IR imaging devices.There is also a continued need to improve the IR sensitivity for gasdetection and signal-to-noise ratio of uncooled IR imaging devices.

SUMMARY

Various embodiments of the methods and systems disclosed herein may beused to provide an infrared (IR) imaging system with high performance incapturing IR images of one or more types of gas in a scene.

An IR imaging device according to one embodiment of the disclosure hasvarious system parameters (e.g., optical and/or non-optical componentsconfigurations) configured detect gas within a narrow wavelength band (arange of wavelengths) of interest. The uncooled IR imaging device (whichfor example may be cooled or uncooled) may be tuned such that the narrowwavelength band corresponds to a type of gas in interest to be detectedwithin the scene.

An IR imaging system according to one or more embodiments of thedisclosure may include an imaging sensor comprising an array of sensorpixels with two spectral responses in the array. A first set of sensorpixels having a first spectral response are configured to detect andimage a gas of interest. A second set of sensor pixels having a secondspectral response are configured to sense radiation outside of the gasdetection bandwidth. In one embodiment, the second spectral band has alower frequency that is above the first spectral band. Read-outintegrated circuit and logic circuitry are configured to generate afirst image of the scene sensed by the first sensor array and a secondimage of the scene sensed by the second sensor array. Gas detectionlogic is configured to detect the presence of gas in the first image, bycomputing the difference between the pixel values of the first image andthe corresponding pixel values of the second image. In one embodiment,if the difference in pixel values exceeds a gas detection threshold thengas is determined to be present at the pixel location. The first imageis modified using the gas presence determinations and difference valuesto enhance the visualization of the detected gas.

In one or more embodiments of the methods and systems disclosed herein,an uncooled infrared (IR) imaging system provides high performancecapturing of IR images of one or more types of gas in a scene, and insome embodiments with a performance that is close to that of a cooled IRimaging device. In one aspect, an uncooled IR imaging device accordingto one or more embodiments of the disclosure has various systemparameters (e.g., optical and/or non-optical components configurations)configured to allow a large percentage (e.g., greater than 90%) of IRradiation within a narrow wavelength band (a range of wavelengths) ofinterest from a scene to hit the imaging sensor of the IR imagingdevice, while substantially blocking IR radiation outside of thewavelength band from reaching the imaging sensor. The uncooled IRimaging device may be tuned in a way such that the wavelength bandcorresponds to a type of gas of interest. As a result, the uncooled IRimaging device may be configured to be highly sensitive to detecting aspecific type of gas of interest within the scene.

In one aspect, for example, an uncooled IR camera system according toone or more embodiments of the disclosure may include: a lens assemblycomprising a set of lens elements having at least one lens coating thatallows at least 90% transmission of IR radiation within a particularrange of wavelengths through the set of lens elements, a filter thatblocks IR radiation outside of the particular range of wavelengths, andan imaging sensor comprising an array of sensor pixels having a pixelpitch greater than or equal to 15 micrometers. In some embodiments, thepixel pitch is greater than or equal to 15 micrometers. In someembodiments, the pixel pitch is greater than or equal to 20 micrometers,or between approximately 15 and 20 micrometers.

The scope of the present disclosure is defined by the claims, which areincorporated into this section by reference. A more completeunderstanding of embodiments of the present disclosure will be affordedto those skilled in the art, as well as a realization of additionaladvantages thereof, by a consideration of the following detaileddescription of one or more embodiments. Reference will be made to theappended sheets of drawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an operating environment in which an infrared (IR)imaging device may operate in accordance with an embodiment of thedisclosure.

FIG. 2 illustrates an exemplary IR radiation path from the scene to theIR imaging device within the operating environment in accordance with anembodiment of the disclosure.

FIG. 3A illustrates radiance levels as a function of wavelength fordetected IR radiation that goes through a gas plume that absorbs IRenergy in accordance with an embodiment of the disclosure.

FIG. 3B illustrates radiance levels as a function of wavelength fordetected IR radiation that goes through a gas plume that emits IR energyin accordance with an embodiment of the disclosure.

FIG. 4 is a schematic of an IR imaging device in accordance with anembodiment of the disclosure.

FIG. 5 is a block diagram of an IR imaging device in accordance with anembodiment of the disclosure.

FIG. 6 is a flow chart for configuring an uncooled IR imaging device inaccordance with an embodiment of the disclosure.

FIGS. 7A and 7B are block diagrams illustrating exemplary super-pixelarray structures in accordance with embodiments of the disclosure.

FIG. 7C is a block diagram illustrating an exemplary super-pixel arraystructures in accordance with an embodiment of the disclosure.

FIG. 8 is a block diagram illustrating an exemplary super-pixel arraystructure in accordance with an embodiment of the disclosure.

FIGS. 9A, 9B and 9C are block diagrams illustrating exemplary biasingconfigurations of an imaging array in accordance with embodiments of thedisclosure.

FIGS. 10A and 10B are block diagrams illustrating exemplary biasingconfigurations of an imaging array in accordance with embodiments of thedisclosure.

FIGS. 11A and 11B are block diagrams illustrating exemplary imagingarrays in accordance with embodiments of the disclosure.

FIG. 12 is a flow chart illustrating an exemplary operation of a gasdetection system in accordance with an embodiment of the disclosure.

Embodiments of the present disclosure and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

Various embodiments of the methods and systems disclosed herein may beused to provide an uncooled infrared (IR) imaging system with highperformance in capturing IR images of one or more types of gas in ascene. In one embodiment, an uncooled IR imaging device (e.g., an IRcamera, a thermal camera, etc.) is configured to detect IR radiationwithin a narrow wavelength band (a range of wavelengths) of interestfrom a scene that hits the imaging sensor of the IR imaging device. Theuncooled IR imaging device is also configured to detect IR radiationwithin a second wavelength band that is outside the gas detection range,and analyze the differences between the two IR images to detect thepresence of a gas of interest.

In one embodiment, the uncooled IR imaging device may be tuned in a waysuch that the wavelength band corresponds to a type of gas of interest.As a result, the uncooled IR imaging device may be configured to behighly sensitive to detecting a specific type of gas of interest withinthe scene. For example, a microbolometer may include an optical cavityformed between an absorber and sensing substrate, which may be tuned toa selected gas absorption/emission band of interest by adjusting theheight between the substrate and the absorber, thereby increasing thesignal to noise ratio. In contrast, conventional microbolometerstypically have a flat, not wavelength dependent, response curve. A tuneddetector with an inherent narrow response curve matched to the gas(e.g., methane) detector spectral response maximum at 7.7 μm may be usedin various embodiments. Furthermore, the imaging sensor may beconfigured to achieve high sensitivity, such as by providing pixels witha pixel pitch optimized for gas imaging.

In addition, the uncooled IR imaging device according to someembodiments may include a logic device (e.g., a processor and/or readoutintegrated circuitry) that is configured to process the captured IRimages to improve the sensitivity, such as by pixel binning, frameaveraging, and noise reduction operations. Using the noise equivalentconcentration length (NECL) (NECL describes the amount of gas to whichan IR imaging device will be responsive) as a metric to measure thesensitivity performance of an IR imaging device, a conventional uncooledIR imaging device may reach 1300 parts per million over meter (ppm×m) ofNECL while a cooled IR imaging device may reach 13 ppm×m of NECL. Usingthe methods and systems of some embodiments described herein, anuncooled IR imaging device may reach a gas sensitivity of 100 ppm×m ofNECL. It is noted that the various configurations of an uncooled IRimaging device in accordance to various embodiments described herein aimto improve the performance under the NECL metric.

Using IR imaging devices to capture a visual representation of a gasrelies on the gas's characteristics of absorbing and/or emitting thermalenergy. For example, a gas may emit thermal radiation in a particularwavelength band against a cold background, in which case the IR imagingdevice provides a visual representation of the gas by capturing a riseof the thermal radiation within the wavelength band around the area inthe scene where the gas is present. A gas may absorb thermal radiationin a particular wavelength band against a warm background, in which casethe IR imaging device provides a visual representation of the gas bycapturing a reduction of thermal radiation in the particular wavelengthband around the area in the scene where the gas is present. Thus,imaging of gas is based on the difference in gas temperature T_(G) andbackground temperature TB, as referred to as gas-to-backgroundtemperature difference ΔT.

FIG. 1 illustrates an environment 100 in which an IR imaging device 170according to one embodiment of the disclosure may operate. An IR imagingdevice 170 is adapted to capture radiation within controllablewavelength bands and thus to produce infrared images (also referred toas “IR images” or “thermal images”), representing a particular selectedwavelength band of IR radiation from a scene 105. Scene 105 comprises ascene background 110 and gas 160 in the form of a gas plume in betweenscene background 110 and IR imaging device 170. Gas 160 is illustratedin the shape of a gas cloud. Scene background 110 has a backgroundtemperature TB 122, and gas 160 has a gas temperature T_(G) 121. It isnoted that a temperature difference ΔT 130 between backgroundtemperature T_(B) 122 gas temperature T_(G) 121 exists as a result ofgas 160 absorbing or emitting thermal energy.

In accordance with one or more embodiments, IR imaging device 170 isconfigured to capture thermal radiation of scene 105 and generate an IRimage representing thermal radiation from scene 105. The thermalradiation of scene 105 includes thermal radiation from scene background110 (represented as T_(B) 122) in combination with thermal radiationemitted and/or absorbed by gas 160 (represented as T_(G) 121).

Specifically, IR imaging device 170 according to one or more embodimentsof the disclosure generates an IR image of scene 105 by capturingthermal radiation from various parts of the scene that hit the imagingsensor of IR imaging device 170. Thermal radiation from different areasof the scene hits different areas on the imaging sensor. As such, someparts of the IR image representing the portion of scene 105 without anyobscurity from gas 160 may include thermal radiation information basedon the thermal radiation solely emitted from scene background 110. Onthe other hand, other parts of the IR image representing the portion ofthe scene 105 that is obscured by gas 160 may include thermal radiationinformation based on both the thermal radiation emitted from scenebackground 110 along with the characteristics of gas 160 to absorband/or emit thermal radiation.

FIG. 2 illustrates, within scene 105, a thermal radiation path 202 fromscene background 110 through gas 160 before hitting the imaging sensorof IR imaging device 170. As shown, thermal energy or IR radiationemitted from scene background 110 travels from an edge of scenebackground 110 at location 204, along the first section of the thermalradiation path 202 before hitting gas plume 160. Once the IR radiationenters into gas plume 160, e.g., at location 206, IR radiation undergoesa change. In the situation where gas 160 has the characteristics ofabsorbing IR radiation within a wavelength band, some of the IRradiation is being absorbed by gas 160, and as such, the radiance levelof the IR radiation within the wavelength band gradually reduces whilethe IR radiation is traveling within gas plume 160, resulting in areduced IR radiation as it exits gas plume 160 (e.g., at location 208)before hitting the imaging sensor of IR imaging device 170. As a result,only a fraction of the thermal energy or IR radiation emitted from scenebackground 110 reaches the imaging sensor of IR imaging device 170. Itis noted that different types of gas may absorb thermal energy or IRradiation in different wavelength bands with different gas absorption oremission strengths. For example, methane (CH₄) has the characteristicsof absorbing thermal energy or IR radiation in a wavelength band between7.0 micrometers (μm) and 8.5 μm. Another type of gas might have thecharacteristics of absorbing thermal energy or IR radiation in adifferent wavelength band. In various embodiments, imaging of differenttypes of gas is a function of based on the gas contrast(gas-to-background temperature difference ΔT) which is a function of thedifference between the background temperature T_(B) and the gastemperature T_(G), gas-path length and gas absorption/emission linestrengths (e.g., wavelength, pressure and temperature dependent).

Graph 300 of FIG. 3A illustrates detected radiance levels of the thermalenergy or IR radiation, which comes through thermal radiation path 202in scene 105 when gas 160 has the characteristics of absorbing thermalenergy, as a function of wavelengths. As shown, the radiance level issubstantially even across the wavelengths except in the wavelength bandbetween v1 and v2. The dip of the detected radiance level in thewavelength band between v1 and v2 is caused by the absorption of thermalenergy or IR radiation by gas 160. As such, if gas 160 includes asubstantial large amount of methane, v1 and v2 would substantiallycorrespond to 7.0 μm and 8.5 μm, respectively.

On the other hand, in the situation where gas 160 has thecharacteristics of emitting IR radiation within a wavelength band,additional IR radiation is being added to the IR radiation from scenebackground 110 while the IR radiation is within gas plume 160. As such,the radiance level of the IR radiation within the wavelength bandgradually increases while the IR radiation is traveling through gasplume 160, resulting in an increased IR radiation as it exits gas plume160 (e.g., at location 208) before hitting the imaging sensor of IRimaging device 170. As a result, the combined thermal energy or IRradiation emitted from scene background 110 and gas 160 reaches theimaging sensor of IR imaging device 170. It is noted that differenttypes of gas may emit thermal energy or IR radiation in differentwavelength bands.

Graph 305 of FIG. 3B illustrates detected radiance levels of the thermalenergy or IR radiation, which comes through thermal radiation path 202in scene 105 when gas 160 has the characteristics of emitting thermalenergy, as a function of wavelengths. As shown, the radiance level issubstantially even across the wavelengths except in the wavelength bandbetween v3 and v4. The spike of the detected radiance level in thewavelength band between v3 and v4 is caused by the thermal energy or IRradiation emitted by gas 160.

Instead of capturing thermal energy or IR radiation across the entire IRspectrum, it has been contemplated that the sensitivity of an IR imagingdevice may be improved by capturing thermal energy or IR radiationwithin a narrower IR wavelength band. As such, an uncooled IR imagingdevice according to one embodiment of the disclosure includes varioussystem parameters (e.g., optical and/or non-optical components)configured to allow a large percentage (e.g., greater than 90%) ofinfrared (IR) radiation within a narrow wavelength band from a scene toreach the imaging sensor of the IR imaging device, while substantiallyblocking IR radiation outside of the wavelength band from reaching theimaging sensor.

FIG. 4 is a schematic of an example of an IR imaging device 400. In someembodiments, IR imaging device 400 is a camera, and more specifically,an IR camera. Additionally, the IR imaging device 400 according to oneembodiment of the disclosure is configured to be optimized for capturingIR radiation within a narrow wavelength band corresponding to a type ofgas. Preferably, the narrow wavelength band has a range of less than orequal to 2 μm. Even more preferably, the narrow wavelength band has arange of less than or equal to 1.5 μm. Depending on the type of gas thatis of interest, IR imaging device 400 can be configured to capture an IRimage within a specific narrow wavelength band that corresponds to thegas in interest. For example, for capturing IR image of methane gas, IRimaging device 400 according to one or more embodiment of the disclosurecan be configured (with various specific system parameters) to captureIR radiation in the narrow wavelength band within a range between 7.0 μmand 8.5 μm.

In some embodiments, IR imaging device 400 has an enclosure 402enclosing the various components of IR imaging device 400. As shown, IRimaging device 400 has a lens assembly 404, an inlet 406, a window 408,a filtering component 410, an imaging sensor 412, and other electroniccomponents 414. Lens assembly 404 includes one or more lens elements416, which together, are configured to optically focus a scene (e.g.,scene 105) from the perspective of the location of imaging sensor 412.As such, the one or more lens elements 416 include refractive propertiesthat redirect IR radiation from the scene (e.g., scene 105) to imagingsensor 412. In some embodiments, lens assembly 404 is fixed onto IRimaging device 170, while in other embodiments, lens assembly 404 isremovable from IR imaging device 170 such that different lens assembliesmay be attached to IR imaging device 170 for different purposes. Forexample, different lens assemblies with different focal lengths and/orzoom capabilities may be interchangeable for IR imaging device 170. Inthis example, lens assembly 404 has a specific focal length that definesa particular field of view (FOV) for IR imaging device 400.

A coating, such as an anti-reflective coating, may be applied to each ofthe lens elements 416. The coating may have the property of reducingreflection of IR radiation from the lens element (that is, improvingtransmission efficiency of IR radiation through the lens element).Different coatings may have different anti-reflection characteristics.According to one or more embodiments of the disclosure, a coating thatis optimized for reducing reflection for IR radiation within thewavelength band(s) of interest is selected to be applied on the lenselements 416.

In some embodiments, the coating can be applied to one or both sides ofeach lens element 416. A coating that allows more than 90% of IRradiation within the narrow wavelength band to transmit through the lenselement 416 may be selected. In some embodiments, a coating that allowsmore than 95% (or even 98%) of IR radiation within the narrow wavelengthband to transmit through the lens element 416 is selected.

It is noted that no matter how efficient the lens elements (even withthe coating as described above) are in transmitting IR radiation, eachlens element reduces transmission of IR radiation to a certain extent.As such, it has been contemplated in various embodiments that lensassembly 404 will include a minimum number of optical elements to meetperformance and costs parameters. In some embodiments, lens assembly 404includes five lens elements or less. It has been contemplated that lensassembly 404 may include two lens elements or less to further improvethe transmission of IR radiation.

IR imaging device 400 also includes a radiation inlet 406 disposed at aconnection point with lens assembly 404. Radiation inlet 406 is anopening (a hole) through which IR radiation that is redirected by lensassembly 404 can enter into the interior of enclosure 402 and ultimatelyto imaging sensor 412. Preferably, radiation inlet 406 has an associatedaperture (a size), and is, in some embodiments, substantially circular(e.g., 90%) in shape. The aperture of inlet 406 determines the amount ofIR radiation that enters into enclosure 402 and reaches imaging sensor412. In order to maximize the amount of IR radiation from scene 105 toreach imaging sensor 412, a large aperture is selected for inlet 406. Insome embodiments, the aperture has an f number (ratio of the focallength specified for lens assembly 404 to the diameter of the inlet 406)less-than or equal to f/2. Even more preferably, the aperture has an fnumber less-than or equal to f/1.5, and even more preferably, less-thanor equal to f/10. In some embodiments, the aperture selected for inlet406 is less-than or equal to f/0.6. In some embodiments, the ratiobetween the focal length and the aperture diameter is selected to be assmall as reasonably practical for gas detection with an uncooleddetector.

According to some embodiments of the disclosure, a window 408 isdisposed at inlet 406. In some embodiments, window 408 covers the entireopening of inlet 406 such that IR radiation that is redirected by lensassembly 404 passes through window 408 before reach other elements, suchas imaging sensor 412, of IR imaging device 400 within enclosure 402.Window 408 can advantageously prevent external particles (e.g., dust)from entering into enclosure 402 that could potentially damage theelectronic components of IR imaging device 400 and/or cause interferenceto capturing images of scene 105. Window 408 may be made of a materialthat has a high efficiency of transmitting IR radiation within theparticular narrow wavelength band. According to one embodiment of thedisclosure, window 408 is made of Germanium.

In some embodiments, a coating, such as the type of coating describedabove by reference to the description of the lens elements, may beapplied to one or both sides of window 408 to further improve theefficiency of transmitting IR radiation. According to one or moreembodiments of the disclosure, the coating is optimized for reducingreflection for IR radiation within the particular wavelength band(s) ofinterest. It has been contemplated that passing only relevant IRradiation (e.g., the IR radiation within the particular narrowwavelength band) to imaging sensor 412 and eliminating other IRradiation from reaching imaging sensor 412 may further improve thequality of the image produced by IR imaging device 400 by increasing thesignal-to-noise ratio of the image. As such, IR imaging device 400according to some embodiments the IR imaging device 400 may also includea filtering component disposed between inlet 406 and imaging sensor 412,configured to allow only IR radiation within the particular narrowwavelength band to pass through while blocking IR radiation outside ofthe particular narrow wavelength band. Filtering component 410 mayinclude one or more filters. In one example, filtering component 410 mayinclude a cut-on filter configured to cut on at the shortest wavelengthwithin the particular narrow wavelength band and a cut-off filterconfigured to cut off at the longest wavelength within the particularnarrow wavelength band. The cut-on/cut-off filters may be made withmaterials and configuration that blocks off (or reflect) any light waveswith wavelengths that are either below (in the case of a cut-on filter)or above (in the case of a cut-off filter) a certain wavelength. Invarious embodiments, the filtering component 410 is configured to selecta desired spectral band by selecting one or more filters based onfiltering criteria including cut-on, cut-off, positions, transmittanceand tolerance of the selected filters. The selection of filters toselect the spectral bands as described herein enhances thesignal-to-noise ratio and reduces unwanted (false alarms) wavelengthdependent effects, e.g., reflectance variations over the spectral bands.In some embodiments, filtering component 410 and window 408 are notseparate elements, but instead they may be combined into one or moreoptical element that is configured to cover inlet 406 and opticallyfilter the incoming IR radiation.

Imaging sensor 412, in some embodiments, may include an IR imagingsensor which may be implemented, for example, with a focal plane array(FPA) of bolometers, micro-bolometers, thermocouples, thermopiles,pyroelectric detectors, or other IR sensor elements responsive to IRradiation in various wavelengths such as for example, in the rangebetween 1 micrometer and 14 micrometers. In one example, imaging sensor412 may be configured to capture images of a very narrow range ofwavelengths. For example, imaging sensor 412 may be configured tocapture images of the particular narrow wavelength band between 7.0 μmand 8.5 μm.

According to some embodiments of the disclosure, imaging sensor 412 haspixels having pixel pitch of at least 20 μm. In other embodiments,imaging sensor 412 has pixels having pixel pitch of at least 25 μm.Having a larger pixel pitch allows each pixel to occupy a larger surfacearea of imaging sensor 412, thereby increasing the area for detecting IRradiation.

Furthermore, similar to lens elements 416 and inlet 406, a coating maybe applied to each individual pixel (detector) in imaging sensor 412.According to one or more embodiments of the disclosure, a coating thatis optimized for reducing reflection for IR radiation within the narrowwavelength band(s) of interest is selected to be applied on the lenselements 416. In some embodiments, the coating applied to the pixels isthe same coating applied to lens elements 416 and inlet 406.

As shown, imaging sensor 412 is communicatively coupled with electroniccomponents 414 disposed within enclosure 402 of IR imaging device 400.FIG. 5 illustrates the various electronic components of IR imagingdevice 400 in more detail. As shown, imaging sensor 412 iscommunicatively coupled with logic device 504 via readout integratedcircuit 502. Readout integrated circuit 502 can be implemented by anytype of integrated circuitry, and is configured to read (or accumulate)a signal (e.g., a current or voltage) indicative of the intensity of thereceived IR radiation at each pixel (detector) of imaging sensor 412 andthen transfer the resultant signal onto output taps for readout. In someembodiments, readout integrated circuit 502 is also configured toconvert the analog current signals into digital data. In otherembodiments, logic device 504 is configured to read the analog outputfrom readout integrated circuit 502 and convert the analog output todigital data. In some embodiments, the digital data includes pixel datacorresponding to the pixels within an image frame or video image frame.The pixels in the image frame may or may not correspond to the pixels(detectors) on imaging sensor 412.

In one example, readout integrated circuit 502 is configured to providea pixel value for each detector on imaging sensor 412. However, it hasbeen contemplated that readout integrated circuit 502 may be configuredto perform a pixel binning processing to further improve thesignal-to-noise ratio of the IR image. For example, readout integratedcircuit 502 may be configured to group adjacent detectors (e.g., a 2 by2 detector block), take a sum or an average of the signals from thosedetectors, and use that value for a single pixel on the image frame. Insome other embodiments, the pixel binning may be performed by logicdevice 504 instead of readout integrated circuit 502.

Logic device 504 may be implemented as any appropriate circuitry ordevice (e.g., a processor, microcontroller, application specificintegrated circuit (ASIC), field-programmable gate array (FPGA), orother programmable or configurable logic devices) that is configured(e.g., by hardware configuration, software instructions, or acombination of both) to perform various operations for IR imaging device400 as described herein. For example, logic device 504 may be configuredto perform pixel binning on image signals received from imaging sensor412 via readout integrated circuit 502 as described above. Logic device504 may be communicatively coupled to (e.g., configured to communicatewith) imaging sensor 412 (via readout integrated circuit 502), controlcomponent 506, memory component 508, display component 510, andcommunication interface device 512.

According to some embodiments of the disclosure, readout integratedcircuit 502, logic device 504, or both may be configured to control theamount of time the signals from pixels (detector) of imaging sensor 412are integrated (e.g., collected) to provide corresponding pixel values(e.g., analog values or digital values) for each image frame or videoimage frame. For example, in microbolometer array implementations ofimaging sensor 412 according to some embodiments, readout integratedcircuit 502 may comprise an integrating amplifier to integrate thesignals from the pixels into a desired range of amplified pixel signalsrepresenting corresponding pixel values. In this regard, readoutintegrated circuit 502 and/or logic device 504 according to someembodiments of the disclosure may be configured to control the durationof such signal integration (also referred to as “integration time”) toprovide a signal-to-noise ratio of the captured IR image that isoptimized for gas imaging.

It has been contemplated to in order to further improve signal-to-noiseratio of the IR image, readout integrate circuit 502 may be configuredto provide a long integration time for capturing each image frame oreach video image frame. According to some embodiments of the disclosure,logic device 504 may be configured to provide an integration time of atleast 1/20 seconds (i.e., capturing video image frames at a speed of 20Hz), or at least 1/15 seconds (i.e., capturing video image frames at aspeed of 15 Hz). In some embodiments, readout integrated circuit 502 maybe configured to provide a shutter speed of at least 1/10 seconds (i.e.,capturing video image frames at a speed of 10 Hz). Depending onembodiments, the integration time may be controlled alternatively oradditionally by logic device 504.

Additionally, it has been contemplated that limiting the rangesensitivity of the detectors of imaging sensor 412 to a narrow dynamicrange may improve the quality of signals obtained at the detectors.Accordingly, readout integrated circuit 502 and/or logic device 504 ofsome embodiments may be configured to provide a narrow dynamic range forthe IR radiation intensity detectable by the imaging sensor 412, such asa dynamic range of 100 degrees Celsius, a dynamic range of 80 degreesCelsius, or even a dynamic range of 50 degrees Celsius. For example,integrating amplifiers, bias circuits, and/or other circuits of readoutintegrated circuit 502 may be configured such that the range of outputpixel values (e.g., in analog or digital signals) in the IR image dataprovided by readout integrated circuit 502 corresponds to a desirednarrow dynamic range (e.g., a range spanning from 0 to 50 degreesCelsius, inclusive). Additionally or alternatively, logic device 504 maybe configured to convert the range of output pixel values in the imagedata to correspond to a desired narrow dynamic range (e.g., a rangespanning from 0 to 50 degrees Celsius, inclusive).

After receiving image data representing image frames (or video imageframes) from imaging sensor 412 via readout integrated circuit 502,logic device 504 may perform additional image processing to the imageframes according to some embodiments of the disclosure, which mayfurther improve the signal-to-noise ratio of the image frames. Forexample, logic device 504 may be configured to perform frame averagingover multiple image frames (e.g., 2, frames, 3 frames, 4 frames, etc.).Logic device 504 may perform frame averaging by generating a new imageframe that takes the average value for each pixel across the multipleframes. Instead of or in addition to frame averaging, logic device 504may also be configured to perform one or more noise reduction algorithms(such as linear smoothing filters, an anisotropic diffusion, wavelettransform, non-linear filters, temporal filtering, spatialfiltering/smoothing, etc.) on the image frames.

As shown in FIG. 5 , IR imaging device 400 may also include othercomponents such as control component 506, memory component 508, displaycomponent 510, communication interface device 512, and/or others.Control component 506 comprises, in one embodiment, a user input and/orinterface device, such as a rotatable knob (e.g., potentiometer), pushbuttons, slide bar, keyboard, touch sensitive display devices, and/orother devices, that is adapted to generate a user input control signal.Logic device 504 may be configured to sense control input signals from auser via control component 506 and respond to any sensed control inputsignals received therefrom. Logic device 504 may be configured tointerpret such a control input signal as a value, as generallyunderstood by one skilled in the art. In one embodiment, controlcomponent 506 may comprise a control unit (e.g., a wired or wirelesshandheld control unit) having push buttons adapted to interface with auser and receive user input control values. In one implementation, thepush buttons of the control unit may be used to control variousfunctions of IR imaging device 400, such as instructing IR imagingdevice 400 to being capturing images of a scene, displaying IR imagesthat has been captured by IR imaging device 400, and/or various otherfeatures of an imaging system or camera.

Memory component 508 comprises, in one embodiment, one or more memorydevices configured to store data and information, including video imagedata and information. Memory component 508 may comprise one or morevarious types of memory devices including volatile and non-volatilememory devices, such as RAM (Random Access Memory), ROM (Read-OnlyMemory), EEPROM (Electrically-Erasable Read-Only Memory), flash memory,hard disk drive, and/or other types of memory. As discussed above, logicdevice 504 may be configured to execute software instructions stored inmemory component 508 so as to perform method and process steps and/oroperations described herein. Logic device 504 may be configured to storein memory component 508 video image frames or digital image datacaptured by the imaging sensor 412.

Display component 510 comprises, in one embodiment, an image displaydevice (e.g., a liquid crystal display (LCD)) or various other types ofgenerally known video displays or monitors. Logic device 504 may beconfigured to display image data and information (e.g., video analyticsinformation) on display component 510. Logic device 504 may beconfigured to retrieve image data and information from memory component508 and display any retrieved image data and information on displaycomponent 510. Display component 510 may comprise display circuitry,which may be utilized by the logic device 504 to display image data andinformation. Display component 510 may be adapted to receive image dataand information directly from the imaging sensor 412 or logic device504, or the image data and information may be transferred from memorycomponent 508 via logic device 504.

Communication interface device 512 may include a network interfacecomponent (NIC) or a hardware module adapted for wired and/or wirelesscommunication with a network and with other devices connected to thenetwork. Through communication interface device 512, logic device 504may transmit video image frames generated at IR imaging device 400 toexternal devices, for example for viewing at a remote monitoring, andmay receive commands, configurations, or other user input from externaldevices at a remote station. In various embodiments, communicationinterface device 512 may include a wireless communication component,such as a wireless local area network (WLAN) component based on the IEEE802.11 standards, a wireless broadband component, mobile cellularcomponent, a wireless satellite component, or various other types ofwireless communication components including radio frequency (RF),microwave frequency (MWF), and/or infrared frequency (IRF) components,such as wireless transceivers, adapted for communication with a wiredand/or wireless network. As such, communication interface device 512 mayinclude an antenna coupled thereto for wireless communication purposes.In other embodiments, communication interface device 512 may be adaptedto interface with a wired network via a wired communication component,such as a DSL (e.g., Digital Subscriber Line) modem, a PSTN (PublicSwitched Telephone Network) modem, an Ethernet device, a cable modem, apower-line modem, etc. for interfacing with DSL, Ethernet, cable,optical-fiber, power-line and/or various other types wired networks andfor communication with other devices on the wired network.

In various embodiments, imaging sensor 412 is an uncooled microbolometerimaging sensor. Gas detection using uncooled microbolometers continuesto pose challenges with respect sensitivity for gas detection. Forexample, a conventional uncooled microbolometer may have the sensitivityto detect gas at the low end of a long wave IR (LWIR) band, e.g., ataround Tum (actual detection range TBR), but may be unable to detect gasat higher wavelengths, such as at around 8 um. Referring to FIGS. 6-12 ,various embodiments of imaging sensor 412, ROIC 502 and logic device 504for increasing gas sensitivity in an uncooled microbolometer imagingsensor are described.

In various embodiments, the imaging sensor 412 includes two or moremicrobolometers having different spectral responses in the same imagingarray, which includes a plurality of pixel sensors arranged in rows andcolumns. The array of pixel sensors includes a first subset of pixelsensors having a narrow spectral bandwidth, with sensitivity down to alower gas detection range (e.g., 7 um), and a second subset of pixelsensors having a wide spectral bandwidth, with sensitivity down to alower range (e.g., 8 um) that is outside the gas detection range (e.g.,a lower range at which the pixel sensors are unable to sense the gas asdetermined by system parameters and configuration).

In various embodiments, the first and second subsets of pixel sensorsare arranged in close proximity to each other on the image sensor 412 inthe same array. The ROIC 502 and logic device 504 are configured toextract pixel values for each of the first and second subset of pixels,respectively. In one embodiment, a first image of the scene isconstructed from the first subset of pixels, and a second image of thescene is constructed from the second subset of pixels. The pixel valuesof the first image correspond to the presence or absence of gas asdetected by the first subset of image sensors.

In one embodiment, corresponding pixel values of the first image and thesecond image are compared and the comparison results are used to enhancethe visualization of the gas presence in the first image, allowing forhigher sensitivity gas detection. For example, pixels of the secondimage may be subtracted from corresponding pixels of the first image,with the magnitude of the resulting values providing an indication ofthe presence or absence of gas at each pixel. In one embodiment, theresulting comparison image (or difference image) may be used to enhancethe first image, producing a higher sensitivity visualization of thedetected gas.

In various embodiments, the ROIC 502 and imaging sensor 412 are arrangedas an imaging array having two or more different bolometers havingdifferent spectral responses within the long wave IR (LWIR) band.Conventional bolometers may have a standard response through the LWIRband and are not sensitive to gas in the scene. By using 2 or morebolometers having different spectral responses, a wide spectral responsebolometer may be used as disclosed herein with increased sensitivity tolower wavelengths in the LWIR band, allowing for response to gas in thescene with greater sensitivity. By placing two different bolometers ofdifferent spectral responses close together on the array, an image canbe formed with standard bolometers while gas detection can be done atthe same time by comparing the output of the wide spectral responsebolometers to the neighboring standard response bolometers and lookingfor large differences.

FIG. 6 illustrates a process 600 for configuring an uncooled infraredcamera to perform optical gas imaging. The uncooled infrared camera ofsome embodiments includes a set of lens elements, an imaging sensor, anda logic device. It is noted that in some embodiments, a subset or all ofthe steps included in process 600 may be performed in order to improvethe optical gas imaging performance of the uncooled infrared camera withrespect to the NECL metric. At step 602, an array of sensor pixels isprovided on the imaging sensor. It has been contemplated that a largepixel pitch in an IR sensor may improve the resulting IR images withrespect to the NECL metric. Even though larger pixel pitches may resultin a lower resolution, it is generally acceptable as gas images have nohigh spatial frequency. The array of sensor pixels has a pixel pitch ofgreater than or equal to 15 micrometers, and in some embodiments,greater than or equal to 20 micrometers. In some embodiments, the arrayof sensor pixels may have a pixel pitch between 20 micrometers and 100micrometers, inclusively. In some embodiments, a coating that increasessensitivity in the spectral region of interest (e.g., 7.0 μm−8.5 μm) maybe applied to each micro-bolometer at the pixel level. In someembodiments, a desired pixel pitch (e.g., pixel pitch greater than orequal to 15 micrometers) can be achieved by binning two or more pixelsthat are of smaller pitch, as would be understood by one skilled in theart.

In various embodiments, a large pixel area may be an advantage when themicrobolometer is used in a narrow band camera. Further advantages areachieved by tuning the optical cavity tuned to the gas band. In thismanner, the gas detector may be designed to be as much signal photonnoise limited as possible and while limiting the other noise componentsin the microbolometer and IC. Binning several pixels also increasessignal-to-noise ratio.

At step 604, at least one coating is applied to the set of lenselements. The at least one coating may be applied to one or bothsurfaces of each lens element in the set of lens elements. As mentionedabove, the coating has the characteristics of allowing at least 90%transmission of IR radiation within a wavelength band (e.g., between 7.0μm and 8.5 μm) through the set of lens elements. The optimized coatingand responses for the narrow spectral range (the narrow wavelength band)further improve the resulting IR images with respect to the NECLmetric).

At step 606, a filter is inserted into the uncooled infrared camera anddisposed between the set of lens elements and the imaging sensor. Insome embodiments, the filter is configured to block IR radiation outsideof the wavelength band. The narrow band pass filter further improves theresulting IR images with respect to the NECL metric (reducing the NECLscore) as it allows high average transmission of IR radiation within thenarrower band. At step 608, a radiation inlet is provided between theset of lens elements and the imaging sensor for allowing IR radiationthat passes through the set of lens elements to reach the imagingsensor. In some embodiments, the radiation inlet has an aperture with afocal ratio less than or equal to f/2 with respect to the focal lengthof the set of elements. In some embodiments, the aperture issubstantially around f/1.

At step 610, the imaging sensor is configured to have a reduced dynamicrange of less than or equal to 50 degrees Celsius. In some embodiments,the reduced dynamic range is equal to or less than 50 degrees Celsius.The reduced (narrowed) dynamic range provides that the digitalizationnoise do not disturb the gas detection. Conventional uncooled IR imagingsystems usually have a dynamic range of 200 degrees Celsius. To avoiddigitalization noise, the dynamic range is preferably less than half ofthe dynamic range of the conventional uncooled IR imaging systems. Atstep 612, the at least one coating is applied to a detector window ofthe imaging sensor and to the sensor pixels to allow at least 90%transmission of IR radiation within the wavelength band through thedetector window of the imaging sensor. The optimized coatings andresponses for the narrow spectral range (the narrow wavelength band)further improve the resulting IR images with respect to the NECL metric.

At step 614, the logic device is configured to capture IR image datawith an integration time of longer than or equal to 1/30 seconds. Insome embodiments, the integration time can be any integration timebetween 1/30 seconds and 1 second. Even more preferably, the logicdevice may be configured to capture image data with an integration timesubstantially equal to 1/15 seconds. The optimized integration time (andframe rate) further minimizes noise in the resulting IR images. However,it has been contemplated that the integration time cannot be too long,as it may produce pink (1/f) noise, which cannot be easily filtered out.

At step 616, the logic device is configured to perform image processingto improve the signal-to-noise ratio of the captured images. The imageprocessing may include pixel binning, frame averaging, and noisereduction, as discussed above.

Referring to FIGS. 7A and 7B, embodiments of arrangements of widespectral response pixel sensors (“W pixels” or “W sensors”) and standardresponse pixel sensors (“S pixels” or “S sensors”) will be discussed.The image pixel sensors are arranged in an image array 700 having thesize of C columns by R rows. The image array 700 of FIG. 7A comprises aplurality of super-pixel arrays 702 of size M×N. For example, a 320×256image array could comprise a plurality of 16×16 super-pixel arrays thatare replicated 20 times across the columns and 16 times across the rows.Within this M×N super-pixel various arrangements of wide spectralresponse pixels “W” and standard response pixel “S” can be obtained. Forexample, to make every other column have different spectral responsebolometers, the super-pixel array, M×N, could be defined with M=2columns of pixel sensors and N equal to the number of rows, R, asillustrated in FIG. 7A. In one embodiment, each super-pixel includes one1×R column of wide spectral response pixels and one 1×R column ofstandard response pixels. Similarly, as illustrated in FIG. 7B, forvarying the spectral response at each row, a super-pixel 712 could bedefined for an array 710 having a size of C columns by 2 rows.

In various embodiments, it is assumed that the wide response bolometersare used for detecting gas and the standard response bolometers areresponsible for showing the image. In such embodiments, it is desirableto maximize the number of standard response bolometers used for imagingand minimize the number of wide spectral response bolometers used todetect gas within the scene. The optimum number of wide vs. standardpixels will vary based on the expected scene, pixel size, optics, andother system configurations and arrangements.

To increase the number of standard pixels, a super pixel of C×M could becomposed of C×1 wide spectral response bolometers (W) and C×(M−1)standard bolometers (S), as depicted in FIG. 7C. Similarly, a superpixel of N×R could be composed of 1×R wide spectral response bolometers(W) and (N−1)×R standard bolometers (S).

In various embodiments, to maximize the number of standard pixels withinthe image array, an M×N super pixel may be composed of only 1 widespectral response bolometer with the remaining pixels being standardbolometers as depicted in FIG. 8 . For example, if the super-pixel were2×2, then 1 pixel would be of wide spectral response and the remaining 3pixels would be standard response bolometers. Other arrangements arealso contemplated, hereunder, such as a checkerboard-like pattern can beused that alternates between wide and standard spectral responsebolometers.

In one embodiment, the ROIC 502 is configured to correctly bias each ofthe two different bolometers so that they produce a uniform scene withminimal output change over the ambient temperature, allowing for maximumdynamic range over a larger ambient temperature range. Depending on howthe temperature compensation is achieved on the ROIC 502, differentconfigurations within the super-cell may be desired. For example, if thetemperature compensation by ROIC 502 is performed on a row basis, then asuper pixel of C×M, composed of C×1 wide spectral response bolometersand C×(M−1) standard bolometers may be used. In this way the 1 row ofwide spectral response bolometers could all be temperature compensatedtogether and the M−1 standard bolometer rows could each have thestandard temperature compensation.

It is known that temperature compensation may be performed with somenumber of reference bolometers, although reference bolometers are notnecessarily required. Thus, if temperature compensation is done per rowas in in the example above, then 1 row of every super pixel will havewide spectral response reference bolometers for temperature compensationand the remaining (M−1) rows will have standard reference bolometers asindicated in FIGS. 9A and 9B. Rather than having a set of references foreach row, 1 global set of wide spectral response reference bolometers(or circuitry) can be switched (MUX) for the 1 row of wide spectralresponse bolometers and another global set of standard referencebolometers (or circuitry) can be switched in for temperaturecompensation of the standard rows (FIG. 9C).

In various embodiments including image arrays having an M×N super pixelwith only 1 wide spectral response bolometer, rows that include bothwide spectral response bolometers (W) and standard bolometers (S) willinclude both sets of biases going through the row so that each of thedifferent bolometers will have the appropriate biasing for temperaturecompensation. This may require extra circuitry and/or reference pixelsin order to provide two different temperature compensation biases at thesame time. Two such embodiments are depicted in FIGS. 10A and 10B.

FIG. 10A shows a block diagram of aspects of an exemplary microbolometerreadout integrated circuit 1000 with bias-control circuitry 1002 inaccordance with an embodiment of the present disclosure. The ROIC 1000includes a microbolometer array comprising a plurality of S sensorsarranged in rows and columns, with at least one row comprising one ormore W sensors and controlled by bias control circuitry 1002. The ROIC1000 may also include additional elements such as timing circuitry, celladdressing circuitry, amplifiers, analog-to-digital converters.

FIG. 10B shows a block diagram of aspects of an exemplary microbolometerreadout integrated circuit 1010 with column control circuitry 1016 inaccordance with another embodiment of the present disclosure. Asillustrated, the ROIC 1010 includes a microbolometer array comprising aplurality of S sensors and W sensors arranged in rows and columns, withone W sensor in every 4×2 block. A multiplexer 1014 is provided for eachcolumn having both W and S sensors for switching between W and S bias ascontrolled by the column control circuitry 1016.

Although row based temperature compensation has been described, it willbe appreciate that this temperature compensation could also beimplemented at the column or pixel level, or a combination of row andcolumn compensation. Also, while these examples focused on biasing thepixel, temperature compensation can also be performed by manipulatingthe bolometer response so that all S and W bolometers can be biased thesame, but manipulation of the signal is done differently for W and Sbolometers in order to maximize dynamic range for each.

Various embodiments of configurations will now be discussed. In oneembodiment, one or more of the two different spectral response tunedbolometers are coated as described herein to filter out electromagneticradiation outside of their respective bands. As illustrated in FIGS. 11Aand 11B, W pixels have higher sensitivity, and the remaining S pixelsare standard pixels. Calibration of the image array may includecorrection on every other line, which would be applied to the next line.In some embodiments, biasing of a column would be difficult, because thecompensation on-chip would be tuned for one bolometer or the other, notboth.

In the embodiments described herein, two different spectral responsetuned bolometers within the same array are described, but it will beappreciated that three or more different spectral response bolometerscould be placed within each super-pixel. Each bolometer would besupplied with the appropriate bias or manipulation of the output signal,or a global setting for all bolometer types may be sufficient.

An embodiment of an operation of various embodiments described hereinwill now be described with reference to FIG. 12 . FIG. 12 illustrates aprocess of performing gas detection in accordance with embodiments ofthe disclosure. As discussed, the image sensor array described hereinincludes sensors having at least two spectral sensitivities. In oneembodiment, the image sensor array includes standard response pixels andwide spectral response pixels, each detecting different bands ofelectromagnetic radiation. At step 1201, image sensor array signals arereceived, such as pixel values provided by the S and W sensors inresponse to detected electromagnetic radiation. In one embodiment, thestandard response pixels, S, are optimized to detect the presence of gaswithin a frequency range, and the wide spectral response pixels, W, areconfigured with a spectral range that is outside the spectral range fordetecting the desired gas.

In one embodiment, the sensor array may be configured to detect widespectral bands, W, of electromagnetic radiation, and other sensor arraysmay be configured to detect narrow spectral bands, S, of electromagneticradiation. For example, the S bands may approximately match one of theabsorption bands (e.g., wavelength ranges) of a known gas. And the Wspectral band may be a band in which the gas is not detected.

Next, in step 1202, sensor array signals are processed for each of thesensor arrays. In this regard, samples corresponding to W sensor arraysignals are passed to block 1203 where the samples are mapped to aglobal W scene coordinate space. In this regard, each W sensor may bemapped to a corresponding coordinate of the W scene coordinate space,for example, by selecting a scene coordinate (e.g., pixel or pixels)having a center that closest matches the center of the correspondingsensor.

Samples corresponding to S sensor array signals are passed to block 1204where the samples are mapped to a global S scene coordinate space. Inthis regard, each S sensor may be mapped to a corresponding coordinateof the S scene coordinate space, for example, by selecting a scenecoordinate having a center that closest matches the center of thecorresponding S sensor.

At block 1205, the mapped samples (e.g., pixel values) provided by the Wsensor arrays for particular scene coordinates are compared to mappedsamples provided by the S sensor arrays for the same scene coordinates.In one embodiment, the two mapped samples are subtracted and thedifference between the two measures provides an indication of thepresence or absence of gas at the particular location in the scene.

In one embodiment, if the difference between a scene coordinate valueprovided by the S sensor array and the W sensor array exceeds a gasdetection threshold, then such value may indicate that a gas is presentat the scene coordinate (block 1207). The presence of the gas may beindicated at the scene coordinate by processing the mapped samples(block 1208) to provide an image 1209 (e.g., a result image) that is,for example, highlighted or color coded at the scene coordinatescorresponding to the identified gas.

In another embodiment, different S sensor arrays may detect Selectromagnetic radiation in different narrow bands. For example, afirst group of one or more S sensor arrays may detect S electromagneticradiation in a first narrow band, and a second group of one or more Ssensor arrays may detect S electromagnetic radiation in a second narrowband that differs from the first narrow band. Additional groups of Ssensor arrays associated with other narrow bands may also be provided.

In another embodiment, one or more S sensor arrays may detectelectromagnetic radiation in multiple narrow bands that match theabsorption bands of multiple gases. In this case, multiple gases withdifferent spectral properties may be detected. Gases may be detectedwith high accuracy using different S sensor arrays directed towarddifferent spectral bands. For example, the different spectral bands maybe associated with different absorption bands of the same gas. Thus, byusing such different S sensor arrays in the process of FIG. 12 , samplevalues (e.g., signal strength) provided by W sensor arrays may becompared with sample values provided by different S sensor arrays 202for different spectral bands.

In one embodiment, each S spectral band has an associated W sensorarray, having a band outside the gas detection range of the gas ofinterest in the S spectral band. In another embodiment, a single Wsensor array is selected for a plurality of S spectral bands. Thus, if agas has multiple absorption bands, then the detection of such bandsusing the different spectral bands may increase the accuracy of gasdetection and reduce the likelihood of false detections (e.g., due tomultiple gases or materials sharing an identical or similar absorptionband).

Where applicable, various embodiments provided by the present disclosurecan be implemented using hardware, software, or combinations of hardwareand software. Also where applicable, the various hardware componentsand/or software components set forth herein can be combined intocomposite components comprising software, hardware, and/or both withoutdeparting from the spirit of the present disclosure. Where applicable,the various hardware components and/or software components set forthherein can be separated into sub-components comprising software,hardware, or both without departing from the spirit of the presentdisclosure. In addition, where applicable, it is contemplated thatsoftware components can be implemented as hardware components, andvice-versa.

Where applicable, the ordering of various steps described herein can bechanged, combined into composite steps, and/or separated into sub-stepsto provide features described herein.

Software in accordance with the present disclosure, such asnon-transitory instructions, program code, and/or data, can be stored onone or more non-transitory machine readable mediums. It is alsocontemplated that software identified herein can be implemented usingone or more general purpose or specific purpose computers and/orcomputer systems, networked and/or otherwise. Where applicable, theordering of various steps described herein can be changed, combined intocomposite steps, and/or separated into sub-steps to provide featuresdescribed herein.

Embodiments described above illustrate but do not limit the disclosure.It should also be understood that numerous modifications and variationsare possible in accordance with the principles of the disclosure.Accordingly, the scope of the present disclosure is defined only by thefollowing claims.

1. An infrared (IR) camera system for optical gas detection, comprising:a lens assembly comprising a set of lens elements having at least onelens coating that allows transmission of IR radiation within aparticular range of wavelengths associated with a gas through the set oflens elements; a filter configured to block IR radiation outside of theparticular range of wavelengths associated with the gas; an imagingsensor comprising an array of sensor pixels; a read-out integratedcircuit (ROIC) configured to provide a first image in a first spectralbandwidth associated with the gas, and a second image in a secondspectral bandwidth where the gas is substantially undetectable; and gasdetection logic configured to detect the gas in the first image, byanalyzing a difference between pixel values of the first image andcorresponding pixel values of the second image.
 2. The IR camera systemof claim 1, wherein the imaging sensor is configured to detect radiationfrom a scene, the imaging sensor comprising an array of super-pixels,each super-pixel comprising a subarray comprising at least one widespectral response pixel having a first bandwidth associated with the gasand a plurality of narrow spectral response pixels having a secondbandwidth outside of a detection range for the gas; and wherein the gasdetection logic is further configured to: generate the first image usingthe radiation detected from the wide spectral response pixels; generatethe second image using radiation detected from the narrow spectralresponse pixels; and detect a presence of the gas in the first image bycomputing a difference between pixel values of the first image andcorresponding pixel values of the second image.
 3. The IR camera systemof claim 2, wherein the ROIC is further configured to performtemperature compensation by biasing each of the at least one widespectral response pixel and the plurality of narrow spectral responsepixels towards producing uniform images in view of an ambienttemperature of the scene; wherein the imaging sensor and/or the ROICfurther comprise a plurality of temperature references comprising a setof sensors and/or reference circuitry; and wherein the temperaturereferences comprise a wide temperature response reference and a narrowtemperature response reference.
 4. The IR camera system of claim 3,wherein the array of super-pixels is configured in a layout comprisingrows of the at least one wide spectral response pixel and rows of narrowspectral response pixels; wherein the ROIC is configured to providetemperature compensation on a row-by-row basis using at least one of thetemperature references to bias each pixel in a corresponding row;wherein the temperature references comprise a global set of temperaturereferences; and wherein the ROIC is configured to switch between a widespectral response reference and a narrow spectral response reference toprovide temperature compensation for each corresponding row.
 5. The IRcamera system of claim 2, wherein the gas detection logic is furtherconfigured to: generate the first image by mapping wide spectrum pixelvalues to a global coordinate space associated with the scene byselecting a scene coordinate having a center that corresponds to thecenter of the corresponding sensor; generate the second image by mappingnarrow spectrum pixel values the global coordinate space associated withthe scene by selecting a scene coordinate having a center thatcorresponds to the center of the corresponding sensor; subtract widebandsamples corresponding to particular scene coordinates from mappednarrowband samples corresponding to the same scene coordinates toproduce a difference value; compare the difference value to a gasdetection threshold to determine a presence or absence of gas at thescene coordinate; and if presence of the gas at the scene is detected,generate a display image comprising the second image of the scene withhighlighted and/or color-coded pixels at the scene coordinatescorresponding to the detected gas.
 6. A system comprising: an imagingsensor configured to detect radiation from a scene, the imaging sensorcomprising an array of super-pixels, each super-pixel comprising asubarray comprising at least one wide spectral response pixel having afirst bandwidth associated with a selected gas and a plurality of narrowspectral response pixels having a second bandwidth outside of adetection range for the selected gas; and a logic device configured to:generate a first image using the radiation detected from the widespectral response pixels; generate a second image using radiationdetected from the narrow spectral response pixels; and detect a presenceof the gas in the first image by computing a difference between pixelvalues of the first image and corresponding pixel values of the secondimage.
 7. The system of claim 6, wherein the imaging sensor furthercomprises a first coating on each wide spectral response pixel providingincreased sensitivity in a spectral region of the gas.
 8. The system ofclaim 6, wherein the imaging sensor further comprises an uncooledinfrared imaging sensor.
 9. The system of claim 6, further comprising aplurality of lens elements defining an optical path; and a radiationinlet provided between the plurality of lens elements and the imagingsensor having an aperture with a focal ratio less than or equal to halfa focal length of the plurality of lens elements.
 10. The system ofclaim 9, further comprising a filter disposed between the plurality oflens elements and the imaging sensor; wherein the filter is configuredto impede radiation outside of the first bandwidth associated with thegas.
 11. The system of claim 6, wherein the logic device is furtherconfigured to reduce a signal-to-noise ratio of the first image and/orthe second image by pixel binning, frame averaging, and/or noisereduction.
 12. The system of claim 6, further comprising a readoutintegrated circuit (ROIC) configured to perform temperature compensationby biasing each of the at least one wide spectral response pixel and theplurality of narrow spectral response pixels towards producing uniformimages in view of an ambient temperature of the scene.
 13. The system ofclaim 12, wherein the imaging sensor and/or the ROIC further comprise aplurality of temperature references comprising a set of sensors and/orreference circuitry; and wherein the temperature references comprise awide temperature response reference and a narrow temperature responsereference.
 14. The system of claim 13, wherein the array of super-pixelsis configured in a layout comprising rows of the at least one widespectral response pixel and rows of narrow spectral response pixels;wherein the ROIC is configured to provide temperature compensation on arow-by-row basis using at least one of the temperature references tobias each pixel in a corresponding row.
 15. The system of claim 14,wherein the temperature references comprise a global set of temperaturereferences; and wherein the ROIC is configured to switch between a widespectral response reference and a narrow spectral response reference toprovide temperature compensation for each corresponding row.
 16. Thesystem of claim 13, wherein the array of super-pixels is configured in alayout comprising rows of narrow spectral response pixels and rowscomprising both narrow spectral response pixels and wide spectralresponse pixels; wherein the ROIC further comprises bias-controlcircuitry configured to selectively apply the narrow temperatureresponse reference and the wide temperature response reference tocorresponding narrow spectral response pixels and wide spectral responsepixels in the rows comprising both narrow spectral response pixels andwide spectral response pixels.
 17. The system of claim 6, wherein thesubarray comprises a plurality of wide spectral response pixelscomprising the first bandwidth associated with a first selected gas anda second bandwidth associated with a second selected gas; and whereinthe logic device is further configured to generate a third image usingradiation detected from the second bandwidth associated with the secondselected gas; and detect a presence of the second select gas in thethird image by computing a difference between pixel values of the thirdimage and corresponding pixel values of the second image.
 18. The systemof claim 6, wherein the logic device is further configured to: generatethe first image by mapping wide spectrum pixel values to a globalcoordinate space associated with the scene by selecting a scenecoordinate having a center that corresponds to the center of thecorresponding sensor; generate the second image by mapping narrowspectrum pixel values the global coordinate space associated with thescene by selecting a scene coordinate having a center that correspondsto the center of the corresponding sensor; subtract wideband samplescorresponding to particular scene coordinates from mapped narrowbandsamples corresponding to the same scene coordinates to produce adifference value; compare the difference value to a gas detectionthreshold to determine a presence or absence of gas at the scenecoordinate; and if presence of the gas at the scene is detected,generate a display image comprising the second image of the scene withhighlighted and/or color-coded pixels at the scene coordinatescorresponding to the detected gas.
 19. A method comprising: generating afirst image of a scene using radiation detected from wide spectralresponse pixels of an imaging sensor, wherein the wide spectral responsepixels have a first bandwidth associated with a selected gas; generatinga second image of the scene using radiation detected from narrowspectral response pixels of the image sensor, wherein the narrowspectral response pixels have a second bandwidth outside of a detectionrange for the selected gas, and wherein the imaging sensor comprises anarray of super-pixels, each super-pixel comprising a subarray comprisinga least one of the wide spectral response pixels and at least one of thenarrow spectral response pixels; detecting a presence of the gas in thefirst image by computing a difference between pixel values of the firstimage and corresponding pixel values of the second image.
 20. The methodof claim 19, wherein generating the first image further comprisesmapping wide spectrum pixel values to a global coordinate spaceassociated with the scene by selecting a scene coordinate having acenter that corresponds to the center of the corresponding sensor;wherein generating the second image further comprises mapping narrowspectrum pixel values the global coordinate space associated with thescene by selecting a scene coordinate having a center that correspondsto the center of the corresponding sensor; wherein detecting thepresence of the gas in the first image further comprises: subtractingwideband samples corresponding to particular scene coordinates frommapped narrowband samples corresponding to the same scene coordinates toproduce a difference value; comparing the difference value to a gasdetection threshold to determine a presence or absence of gas at thescene coordinate; and generating a display image comprising the secondimage of the scene with highlighted and/or color-coded pixels at thescene coordinates corresponding to the detected gas.